A container, open at the top, is in the form of a frustum of a cone of height 24 cm with radii of its lower and upper circular ends as 8 cm and 20 cm respectively. Find the cost of milk which can completely fill the container at the rate of Rs 21 per litre.
Sol :
h = 24 cm
lower end = r = 8 cm
upper end = R = 20 cm
V =π×h3×(R2+R×r+r2)
V = π×243×(202+20×8+82)
V = 176 / 7 x 624
V = 176 x 89.142 cm3
V = 15688.992 cm3
V = 15688.992cm31000
V = 15.688992 litre
Cost of milk per litre fill the container = 21 Rs
∴ Total cost of milk fill the container = 15.688992 x21 = 329.4688rs